Leucascandrolide A is a marine natural product, which attracted considerable attention due to the unique molecular constitution, potent cytotoxic properties and ambiguity of the biogenetic origin. The objective of this competitive supplement to our grant R01 CA93457 is to establish the cell culture facility and the environment in order to conduct comprehensive cell-based evaluation of leucascandrolide A aimed at the determination of the mode of action of this highly cytotoxic natural product. These objectives are beyond the scope of our original application, which was centered on the development of efficient chemical synthesis of leucascandrolide A, construction of synthetic analogs and development of several new synthetic methods. Our preliminary studies have demonstrated highly potent and broad cytotoxicity profile. Furthermore, leucascandrolide A had no noticeable effect on disrupting either tubulin or actin microfilaments, strongly suggesting an alternative mechanism of action. Within the scope of this project we will pursue (a) broad evaluation of cytotoxicity and toxicity of leucascandrolide A. (b) determination of the structure activity profile, and (c) design of reagents for affinity-based isolation of the cellular target of leucascandrolide A. [unreadable] [unreadable]